Ever since blood was recognized as the life-sustaining fluid, and as the science and technology progressed, it has been a goal of human ingenuity to produce an artificial substitute for blood. Toward this goal, Mulder et al. (1934, J. Cell. Comp. Physiol. 5:383-397) used purified human hemoglobin from outdated blood and performed the first experiment for testing the cell-free hemoglobin as a temporary blood substitute. In 1976, Moss et al. (1976, Surg. Gynecol. Obstet. 142:357-362) repeated Mulder et al's supra experiment and confirmed the observation that cell-free hemoglobin could serve as an effective oxygen carrier, although oxygen delivery to tissues was lower than normal.
Several approaches were then taken to solve the problem of altered oxygen affinity of the cell-free hemoglobin. One of the approaches was to covalently attach pyridoxal phosphate to the amino terminus of the .beta.-globin polypeptide (R. E. Benesch et al., Biochem. 11:3576 (1972); G. S. Moss et al., Surgery 95:249 (1984); L. R. Sehgal et al., Surgery 95:433 (1984)). A second approach was to stabilize the hemoglobin tetramers normally formed in erythrocytes, by chemical crosslinking. (Snyder et al., 1987, Proc. Natl. Acad. Sci. USA 84:7280-7284; Moss et al., 1988. Biomat. Art. Cells, Art. Org. 16:57-69).
Although intramolecular crosslinking significantly improved stability, hemoglobin was detectable in the urine of experimental animals and nephrotoxicity was observed as a side-effect.
Further advance was made when Gould et al. (1990, Ann. Surg. 211394-398) demonstrated that polymerized, pyridoxylated human hemoglobin is well-suited as an efficient oxygen carrier and temporary blood substitute.
Even though these advances are significant, an important limiting factor that must be recognized is that the source of human hemoglobin is blood and human blood is in short supply. Furthermore, the risk of contamination of the blood with such agents as the hepatitis and human immunodeficiency viruses is an omnipresent problem, particularly when large amounts of human blood from a variety of different sources is to be handled in a production-type facility.
Recently Nagai et al. (1985, Proc. Natl. Acad. Sci. USA. 82:7252-7255) and Ryan et al. (1990, Science 245: 971-973) demonstrated an alternative approach by synthesizing human hemoglobin in non-human host by recombinant DNA technology.